'Twerp' & 'twit' seemed slow migrating to Oz if they were current there in 60s, as stated above. I remember them here in England from 1940

Rich-joy commented on their currency, rather than their onset, in the OZ 60s; I recall them both being current in Melbourne in the 40s but perhaps the circles I moved in were more vulgar than hers. "Nong" was also current around me at that time and occasionally applied to me by my father, who wanted me to be less bookish and more "hands on" in the ways he was.

I don't recall hearing "dickhead" before the 60s but when it appeared it was accompanied (in more polite conversation) by Richard Cranium.

Cheers, Rowan